Possible? Sure. Plausible, probably not, but at this point, who knows. If it was me I would try balancing the tires again, and maybe switching back to front, or side to side. One other thing I might try is to put some wood blocks or something between the axle and frame at about the level it was at before. If it's in the axle you'll probably feel the vibration worse. If it goes away it might be the pinion angle or u-joint angle.
As a last resort, try and flush the blinker fluid.
http://kalecoauto.com/index.php?main...products_id=22
Or maybe these cross drilled brake lines will do the trick...
http://kalecoauto.com/index.php?main...products_id=39
This might be pretty obvious, and I don't want to insult your intelligence, but in case you haven't done it yet, the muffler bearings might have a flat spot...
http://kalecoauto.com/index.php?main...products_id=48
But this tool is by far the one I use the most and have had real good results with...
http://kalecoauto.com/index.php?main...&products_id=7
I'd let you borrow mine, but they are cheap enough that every man should have one in his toolbox.